The invention relates to an electrode configuration for gas-forming electrolytic processes, in particular for processes in membrane cells, comprising a planar electrode structure having at least two electrically conducting and mechanically firmly interconnected electrode elements, between each of which is provided a gap for the escape of gas. The electrode elements along the gap have supporting surfaces for an ion exchanger membrane or a diaphragm and where edge areas bordering the gap are designed for the escape of gas.
A membrane electrolysis cell of the filter press type with planar-structure electrodes in pairs is known from DE-OS 32 19 704, to which U.S. Pat. No. 4,469,577 corresponds, wherein the electrodes each have at least one perforated active central portion and wherein a membrane is disposed between the paired electrodes; in each case a seal is disposed between electrode edge and membrane edge. The perforated central portion of the electrodes has a lattice-like structure, where the lattice bars of the paired electrodes are offset against one another by a maximum of half a lattice bar width and the lattice bars of one electrode are positioned such that their distance apart is less than the projection of their width. The lattice bars have at least on their active side a convex curvature, where the thickness of the seal between the electrode edge and the membrane edge is equal to or less than the height of the lattice bar portion projecting above the electrode edge. One problem is that in a configuration of this type a depletion and also gas bubbles in the vicinity of the support surface must be expected, resulting in unfavourable effects on the membrane and the electrode coating.
The electrolysis cell is intended for electrolysis of an aqueous halogenide-containing electrolyte, for example brine, in order to produce an aqueous alkali metal hydroxide solution plus halogen and hydrogen.
In cells structured in this way, a chloride depletion must be expected in the vicinity of the point of contact between the electrode and the membrane, thereby resulting in a drop in the long-term stability.
An electrode configuration for gas-forming electrolysers, in particular for membrane electrolysers, is known from EP-PS 0 102 099, to which U.S. Pat. No. 4,474,612 corresponds, having vertically disposed plate electrodes, a back electrode and a membrane between the two electrodes. The plate electrode is divided here into horizontal strips, the entire active electrode surface of which is disposed parallel to and at a very short distance from the back electrode, but with a gap being provided between the membrane and the electrode for the escape of the gas generated by the electrochemical transformation process. In order for the gas rising from the electrode gap to escape, the horizontal strips are each provided in the vicinity of their top edges with an angled gas escape element at which the rising gas expands and part of which is routed to behind the electrode.
The electrode gap between the membrane and the two electrodes that is always necessary for the gas to escape proves to be a problem here, as this relatively large electrode spacing also entails an increase in the cell voltage.
An electrode configuration for gas-forming electrolysers is known from DE-OS 36 40 584, to which U.S. Pat. No. 4,839,013 corresponds, in particular for monopolar membrane electroiysers having vertically disposed plate electrodes plus back electrodes and a membrane between plate electrode and back electrode. Electrically conductive planar structures connected in electrically conductive manner to the plate electrodes on those surfaces of these electrodes facing the membrane are known as pre-electrodes, and run in parallel planes to the plate electrodes.
The planar structure used as an electrode is designed in the form of perforated plates, expanded metals, wire fabrics or wire meshes, with the spacing of the planar structures ranging from 1 to 5 mm; the plate electrodes are horizontally divided all the way through into several separate units in order to improve the current distribution in the membrane and to reduce the voltage drop on the surfaces facing the membrane.
The problem with such electrodes is the chloride depletion, in particular in the vicinity of the point of contact between electrode and ion exchanger membrane, thereby resulting in a reduction in the long-term stability.
Furthermore, a process for electrolysing liquid electrolytes by means of perforated electrodes in electrolysis cells divided by the ion exchanger membrane is known from EP-OS 0 150 018, to which U.S. Pat. No. 4,627,489 corresponds, in which a gas area is created by gas bubble formation lateral to the main flow direction of the electrolyte. After bursting at the phase boundary, the resultant gas bubbles transfer their gas content to the adjacent gas area lateral to the main flow direction, said area being formed by the rear space behind the electrode in the case of plate-like electrodes. The perforated electrodes can comprise expanded metals or sheet metal strips, among other materials.
In configurations known from EP-OS 0 150 018, the relatively expensive structure based on electrodes with gas-flow-guiding elements comprising single sheet metal strips presents problems.